Telephone-exchange system



May 8, 1928. v1,668,687 F. K. LOW

TELEPHUNE EXCHANGE SYSTEI Filed June 9; 1927 5y @Jmw Patented May 8., 1928. l

UNITED STATES PATENT oFFlcE.

FRANK X. LOW, OF BROOKLYN, NEW YORK, ASSIGNOR T WESTERN ELECTRIC OOI- PANY, INCORPORATED, 0F NEW YORK, N. Y., A CORPORATION 0F NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application led June 9, 1927. Serial No. 197,589.

This invention relates to telephone exchange systems, and more particularly -to means in an exchange system employing machine switching apparatus controlled from -a subscribers 'substation dial, for enabling subscribers at substations remotely removed from a machine-switching oiiice to which its vline terminates to control said apparatus accurately. y

In most telephone systems, the exchange area is so divided into oice areas that each bice is located so that itis central to the c subscribers lines which it serves, and therefore the subscribers lines are of substantially equal length and relatively short.

, The ohmic resistance and capacity of subscribers lines is thereby made low so that the apparatus at the oiiice which responds to impulses dialed by subscribers 1s enabled to respond accurately with a minimum of failure due to the impulses being mutilated during transmission over the subscribers zWhere it is found necessary to serve a subscriber who is located at a considerable` distance from an oice, and whose line would consequently have considerable resistance, and capacity, it is desirable to provide more sensitive impulse responsive apparatus to receive the impulses dialed by the subscriber, and to repeat them to the selectors or other impulse -recording apparatus of the oiiice.;

A This is particularly desirable, as then the precise adjustment of the subscribers dial for sending impulses for the most eiiicient ratio of circuit closing and circuit opening periods is not so necessary. The present invention relates to :1 circuit which may be inserted at the exchange oice between the external line extending to the subscribers station and the internal line terminating in the usual exchange apparatus, whereby, re-vY 1 gardless of the extentof multilation of the impulses dialed Aeither through the poor ad]ustment of the dial or through the attenuating effect of the line characteristics,

the impulses repeated into the oice appa'- ratus shall be of proper strength and character to accurately operate the apparatus of the oiiice.

In accordance with the specific embodiment of the invention, chosen by way of illustration, the long subscribers line is provided with a very sensitive impulse responsive relay which is adjusted to quickl -and accurately follow the impulses diale and which in .turn controls an improved impulse repeating relay. The impulse repeating relay has two windin s, one, a primary or operating winding w ich is controlled directly from contacts of the impulse responsive relay, and the other, a secondary windin controlled through its own contacts and a ected by the charging and discharging current through a condenser. The effeet of the secondary winding as controlled by the condenser is such that shouldthe operating make impulse through vthe pri= mary winding of the relay be short, the charging current through its secondary windin and through the condenser will tend to hol the relay operated after the circuit of its primary winding is broken, for an interval predetermined by the capacity of the condenser, the number oi' turns in the secondary winding, and the resistance of the charging circuit, so that the make period of the impulse repeated by such relay will be longer than the make period of the impulse received over tlie subscribers line. If, however, the make impulse received over the suhn scribers line is long, the impulse repeated will be lon also, since the repeating relay will not re ease until the operating circuit through its primary winding is broken.

On the other hand,.when an open period occurs in the line circuit during dialing, the repeating relay deenergizes, providing a discharge path for the condenserthrough its secondary winding and back contact to ground through resistance, the direction of the discharge current being such that the iux set up is. opposite in direction to the iiux set up by the primary winding when the relay is energized. If, then, the open p eriodbetween input impulses is too short, the repeating relay is retarded in operat- 'ing following the o n periods due to the opposing eiect of t e secondary winding,

and therefore 'the open period between the repeated impulses'will be long. If the open riod between the impulse-s received is long,

owever, the open period between repeated impulses will be long, but not longer than the eriod between received impulses, since by t e time the primary circuitof the repeating relay is closed, the elect of the discharge current throu h the secondary winding will have subsied and the relay will no longer be delayed in operating.

Referring to the drawings for an illustration of the invention,

Fig. 1 shows a subscribers line terminating at a machine switching oilice in-a longline vequipment embodying the present invention; and

Fig. 2 discloses charts illustrating the manner in which the relay of the invention functions.

The subscribers substation shown at 1 is of the usual type equipped with an impulse dial 2. The subscribers line, having conductorsl 3 and 4, is assumed to be of considerable length havingy a maximum loop resistance which`- may be as high as 1700 ohms, and is shown terminating in special long line equipment at the central machine switching oiiice. The long line equipment is shown at the right of Fig. las being provided with the usual line and cut-off relays and with final selector multiples. The line conductors extending to the right margin of Fig. 1 may be terminated in a line linder bank and start circuit of the type disclosed in the patent to W: H. Matthies, No. 1,567 072, granted December 29, 1925. The exchange apparatus for extending connections from and to the calling subscribers line may be of the well known type such as is disclosed in the patent to Matthies above referred to, and as disclosed in the patent to F. A. Stearn, 1,505,171, granted August 19, 1924.

' t is believed that the invention will beA best understood from a detailed consideration of the circuit disclosed in Fig. 1 and from a description of the manner in which it functions.

When the calling subscriber at sub-station 1 removes his receiver from the switchhook to initiate a call, a circuit is closed forthe impulse relay 5, which extends from battery through the right winding of relay 5, the lower left Winding of repeating coil 6,`the lower back contact of relay 7, over line con- 'ductor 4, through the substation 1, returning over line conductor 3, the upper back Contact of relay 7, the upper left Winding of repeating coil 6 to ground through the left winding of relay 5. Relay 5 energizes over this circuit, and at its front contact closes a circuit for the impulse repeating relay 8, extending from battery through resistance 9, the contact of relay 5, the left back contact of relay 10, to ground through gizes and simultaneously closes both of itsv ront contacts at its left contact closing a bridge across the Vinternal line conductors 11 and 12, and through the winding of line relay 13, which may be traced from battery through the Winding of\relay l3,`the left back contact of cut-olf relay 14, conductor 12, the lower right Winding of repeating coil 6, the left contacts of relay 8, the upper right winding of repeating coil 6, conductor 11 to ground through the right back contact of cut-off relay 14. The operation of line relay 13 causes, in the well known manner, the connection of the subscribers line to a district selector and sender in preparation for the selection of the desired line.

the Winding of relay l0, from the linal multiple sleeve conductor 17, and at its front contact connects the sleeve conductor 17 through resistance 18 to battery, thereby marking the multiples of the subscribers line as busy at the banks of all final selectors having access thereto. Relay 16 also connects. the condenser 19 between the sleeve conductor 15 and the sleeve conductor 17 for the purpose of passing a checking tone if required, disconnects at its left back contact, the bridge across conductors 11 and 12 comprising thc condenser 2O and ring-up relay 21, and at its left front contact connects the protecting conductor 22 and resistance 23 in series in bridge of the left or impulsing contacts of repeating relay 8- in preparation for repeating the dial impulses. At this time, a circuit has been extended through thc left contacts of relay 8 and over conductors 11 and 12 into the district selector trunk circuit and thence to the impulse relay of the selected sender in the manner described in the patent heretoforel referred to.

The vsubscriber may nowproceed to dial the number of the desired subscriber by manipulating his dial 2. Upon the first break in the loop circuit over conductors 3 and 4, relay 5 deenergizes quickly, opening the energizing circuit through the left Winding of repeating relay 8. It is to be noted at this point that when relay 8 cnergizeda charging path was closed for the condenser 24, from battery through resistance 25, the

a direction as to aid the left win in v path for the condenser, which extends from ground through the right winding of relay 8, condenser 24, right armature,'and back contact of relay 8 to ground through resistance 26. If the repeating relay 8 is not again energized within a definite time interval, the condenser 24 Vwill thus become fully discharged and the flux set up by the dischar ing current through the right winding of re ay 8 will become entirely dissipated.

On the next closure or 'makeof the dial contacts, relay 5 again energizes, in turn energizing relay 8 which again closes the bridge circuit across conductors 11 and 12. This operation continues as the dial 2 returns to normal upon each manipulation in accordance with the several digits of the desired line number. l When dialing is completed and the connection has been established to the line of the desired subscriber, relay 5 `is maintained energized over the calling line Yand talking current is supplied tothe calling subscribers substation through the left windings of repeating coil 6. Relay 5 holds relay8 energized during conversation and these relays therefore function as supervisory relays under the control of the calling subscriber.

In order that the impulse correcting functions ofrepeatng relay 8 may be most clearly understood, it will iirst be assumed that the impulses as received by the relay 5 have a minimum percentage of break interval to make interval, that is, that the intervals during which the subscribers loop is closedv between impulses are too long compared 'with the intervals during which the loop is opened. In Fig. 2 two charts have been disclosed, the one at the left illustrating the condition assumed above. At the top of this chart the input impulses received by the relay 5 have been shown at A as having long make periods as compared with the periods between impulses. Since the relay 5 follows very closely the impulses received, and repeats them correspondingly to the primary winding of relay 8, the current in the left or primary winding of relay 8 will assume the general form shown at C.. Upon each energization of relay 8, the condenser 24 char es through the secondary or right win ing of the relay, causing\a current in the secondary winding, which, during a portion of the time that the relay is energized over its primary winding, aids in the energizationof the relay. During the open period between impulses, when there is no current flowing in the primary winding of relay 8; and the relay is deenergized, the condenser 24 `is discharging, causingv current to flow in the opposite direction through the secondary winding. The current through the secondary winding is thus in the form shown at D.Y The resultant eiiect of the current in both windings othe relay is shown at E, the curve being a composite of the curves shown at C and D. It will be noted from an analysis of the curve E, that at the points marked 200, the discharge of the condenser 24 through the secondary winding of" relay 8 has opposed the primary winding of relay 8 since the break period between impulses was too short, and that the relay is thereby delayed -inK reenergizing. The resultant impulses repeated by the left contacts of relay 8 therefore take the form disclosed at B, which form is -far better for accurate operationof the pulsing 'relay of the central oiic sender than the input impulses s hown at i It will now be assumed that the impulses as received by the relay 5 have a maximum percentage of break interval to make interval, that is, that the intervals during which the subscribers loop is closed between impulses istoo short compared with the intervals during which the loop is opened. In the chart at the right of Fig. 2 'this condition has been illustrated. At the top ofthis chart the input impulses received vby the relay 5 have been shown at A as having short make intervals as compared with the intervals between impulses. At C the curve of the current tlowlng through the primary winding of relay 8 has been illustrated as following accurately the input impulses. Again, upon each energization of relay 8, the condenser 24 charges through the secondary winding of this relay thereby aiding the primary winding to hold the relay energized slightly after its primary circuit is broken and upon each deenergization of relay 8, the condenser 24 discharges in the opposite direction through the secondary winding ofthe relay to oppose the primary winding. The curve of the current in the secondary winding is shown at D, and the resultant effect of the two windings is illustrated by the curve E. It will be noted from an analysis of the composite curve E that since the periods during which the primary windingof relay 8 is energized are very short, that the secondary winding tends to set up a flux at points 201, which is sufficient to hold the relay operated for an interval after each openimpulses have been assumed to belong comv energizes. rIfhe output pared with the make periods, the condenser 24 has time to fully discharge each time -that the relay 8 deenergizes be ore the primar circuit of the relay becomes again close Thus the secondary winding has no effect upon the quickness witinwhich the relay 8 i pulses repeated by the relay 8 will therefore have the form indicated at B which, in comparison wlth the input impulses shown at A, have their make and break periods more evenly divlded. It is thus apparent that relay 8 acts to correct the form of the impulses received and to repeat them in a form which is better adapted for accurate reception of the central station apparatus. I y

When the long line circuit shown in Fig. 1 is seized by a final selector, a busy condltion is placed on the sleeve multiple 17 at the final selector causing the operation of relay 10. Relay 10 upon operating disconnects, at its right back contact, relay 16 from the sleeve conductor 15, land connects the sleeve 15|'over its right front contact through resistance 18 -to battery, making the line busy at the bank multiples of line finders in which it terminates. At its left armature contacts, relay 10 transfers the battery con-V nection at the front contact of relay.5 from the leftto the rightpwinding of relay 8, thereby reducing current drainduring conversation. Y

When ringing current isE applied to the tip and ring conductors 11 and 12 over the final multiples from the incoming selector (not shown), relay 21 operates over a circuit which may be traced in part from conductor 11, the upper right winding of repeating coil 6, condenser 20, winding of relay 21, the left back contacts of relay 16, the lowerright winding of repeating coil 6, to conductor 12. Relay 21 responds to the ringing current and at /its contact closes an obvious circuit for relay 7. Relay 7 energizes upon each application of ringing current from the incoming selector, and at its back contactsdisconnects the windings of relay 5 from the line conductors 3 and 4, and at its froutcontacts extends the conductors 11 and 12 directly to the conductors 3 and 4 respectively, so that ringing current may pass directly over the subscribers external line to the substation bell. As soon as the subscriber responds, ringing current is tripped at the incoming selector in the usual manner, whereupon relay 21 remains deenergized and relay 7 releases toreconnect the left windings of repeating coil 6 land the windings of relay 5 with the line conductors 3 and 4. Relays 5 and 8 now energize, talking current being supplied to the line from the repeating coil 6. Supervision is controlled by the bridge' established at-the left "-conta'ctsof relay 8 and, through relay 5,- is

under the control of the subscriber at subvstation 1.

What is claimed is:

1. A relay having a primary and a second ary winding, an energizing circuit extending through said primary winding, a condenser, a charging path for said condenser extendin through a front contact of said relay and through said secondary winding, and a discharge pathfor said condenser extending through the back contact of said relay an said secondary winding.

2. A relay having a primary and a sec- 4 3. A relay having a primary and a secondary winding, an energizing circuit extending through said primary winding, a condenser, a battery, resistances, a chargin path for said condenser extending from said battery through one of said resistances, a

front contact on said relay and through said secondary winding, and a dischar e path for said condenser extending through said secondary winding, a backcontact on said relay, and through a second of said resistances \to ground.

4. A relay, an energizing Winding therefor, and means for rendering said relay slow to release only when its energizing circuit is closed for an interval shorter than a.

prescribed interval and for rendering said relay slow to energize only when reenergized after an interval shorter than a prescribed interval.

5. A relay, a primary. .winding therefor, an energizing circuit extending through said winding, a secondar controlled by said re ay for energizing said secondary winding in such a manner that said relay is rendered slow to release only when the energizing circuit of its primary winding is closed for an, interval shorter than a prescribed interval and that said relay is rendered slow to energize only when reenergized after an; interval shorter than a prescribed interval.

6. A relay, a primary Winding therefor, an energizing circuit extending through said winding, a secondary winding, a condenser, and means controlled by said relay for winding, and meansv charging and discharging said condenser manner that said relay is rendered slow to release only when the energizing circuit of its primary Winding is closed for an'interval shorter than a prescribed interval, and that said relay is rendered slow to energize only when reenergized after an interval shorter than a prescribed interval;

7. A relay, a primary Winding therefor, an energizing circuit extending through said winding, a secondary winding, a condenser, means controlled by said relay for charging and discharging said condenser through said secondary Winding in such a manner that said relaydis rendered slow to release only When the energizing circuit of its primary Winding is closed for an interval shorter than the charging time of said' condenser, and that said-relay is 'rendered slow to energize only when reenergized after an interval shorter than theldischarging time of said condenser, and means for controlling the Vsaid relay is rendered slow to release only when the energizing circuit of its primary winding is closed for an interval shorterthan the charging time of said condenser, and that said relay is rendered slow to energize only when reenergized after an interval shorter than the discharging time of said condenser, and resistances for controlling the charging and discharging times oi' said condenser.

In witness whereof, I hereunto subscribe my name this 27 day of May, A. D. 1927.

FRANK K. LOW. 

